Notice: This page requires JavaScript to function properly.
Please enable JavaScript in your browser settings or update your browser.Leer How many unique? | Selecting
SQL Basics
course content

Cursusinhoud

SQL Basics

SQL Basics

1. Selecting
The very first meet with the databaseSELECTing certain columnsLIMITing resultsUnique values from columnUnique values from multiple columnsHow many?How many unique?AliasesTables aliases
2. Filtering
Word filteringNumber filteringCombining conditionsFiltering by numeric intervalMultiple filtering on one columnLIKE filteringNOT like this!
3. Aggregating
MINimal and MAXimal valuesSUMming valuesMean valuesROUNDing
4. Sorting
Sorting by one columnSorting in DESCending orderThe cheapest carSorting by multiple columns
5. Grouping
What is grouping?More aggregate statistics!Grouping by multiple columnsThe cheapest combinationHAVING some conditionsLeast consuming carsFiltering group size
6. Practicing
Challenge: Unique combinationsChallenge: Average Q-series cars priceChallenge: The cheapest new A-series carsChallenge: Relation between engine size and fuel consumptionChallenge: Mileage and manufacture year - is there relation?Challenge: Average price for each model and yearChallenge: The most expensive transmission + engine size combinations

book
How many unique?

But what if we want to calculate the number of unique site visitors? Sounds like a combination of selecting unique and then counting...

Yes, that's the point! To calculate the number of unique observations over a certain column use COUNT(DISTINCT( ... )) statement. For example,


              
12

            
SELECT COUNT(DISTINCT(user_id))
FROM visitors
copy

This query will return a single value - the number of unique user_id in the visitors table.

Taak

Swipe to start coding

Count the number of different cars models in the audi_cars table.

Oplossing

Switch to desktopSchakel over naar desktop voor praktijkervaringGa verder vanaf waar je bent met een van de onderstaande opties
Was alles duidelijk?

Hoe kunnen we het verbeteren?

Bedankt voor je feedback!

Sectie 1. Hoofdstuk 7
toggle bottom row

book
How many unique?

But what if we want to calculate the number of unique site visitors? Sounds like a combination of selecting unique and then counting...

Yes, that's the point! To calculate the number of unique observations over a certain column use COUNT(DISTINCT( ... )) statement. For example,


              
12

            
SELECT COUNT(DISTINCT(user_id))
FROM visitors
copy

This query will return a single value - the number of unique user_id in the visitors table.

Taak

Swipe to start coding

Count the number of different cars models in the audi_cars table.

Oplossing

Switch to desktopSchakel over naar desktop voor praktijkervaringGa verder vanaf waar je bent met een van de onderstaande opties
Was alles duidelijk?

Hoe kunnen we het verbeteren?

Bedankt voor je feedback!

Sectie 1. Hoofdstuk 7
Switch to desktopSchakel over naar desktop voor praktijkervaringGa verder vanaf waar je bent met een van de onderstaande opties
Onze excuses dat er iets mis is gegaan. Wat is er gebeurd?
some-alt